Coagulation of finely divided suspended solids



Aug. 3, 1954 J.E. cRos'lsLEY coAGULATIoN oF FINELY DIVIDED SUSPENDEDsoLIDs Filed June 27, 1951.

`2 Sheets-Sheet 1,

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Aug. 3,.v l` 954 COAGULATION Filed lJune 27, 1951 /27v 95 /lz 92 /laJ..E. cRossLEY OF' FINELY DIVIDED SUSPENDED SQLIDS 2 Sheets-Sheet 2FIGA..

INVENTOR.

JAMES E. CROSSLEY avia ATTORNEY.

Patented Aug. 3, 1954 CAGULATION OF FIN ELY DIVIDED SUSPENDED SOLIDSJames E. Crossley, Collinsville, Ill., assignor to Allied Chemical t DyeCorporation, New York, N. Y., a corporation of New York Application June27, 1951, Serial No. v233,757

3 Claims. 1

This invention is directed to improved method l"and means for separationand recovery of liquids from finely divided material suspended therein.More particularly, it is concerned with `such separation procedures inwhich a flocculat- .ing agent is employed to assist the removal offinely divided insoluble material from suspensions in liquid orsolutions.

In separating suspended material and recovery of clear solutions from e.g. slurries or muds, it has been the practice tostore the liquidsuspension in large vats to permit settling, whereupon clear liquor iswithdrawn by decantation. The solid particles are frequently in such afine 4,state of subdivision that use of prolonged periods ofsettlingprior to decantation and consequent large volume of settling-decantationvessels are required. It will be appreciated that from the standpoint ofkeeping plant investment. at a minimum, affording maximum output ofproduct from a given installation and providing flexibility ofoperation, the long settling time and resulting large volume of tanksare serious disadvantages. Various methods, such as diluting the fslurry with greater amounts of' water in order to increase the diierencein density between solution and mud particles and thereby effect anincrease in rate of mud settling, have been proposed. However, when itis desired to recover the solution components in concentrated form,resorting to dilution of the mud with water causes a decrease in economyof operation by reason of increased steam costs in evaporating vsaidwater in subsequent operating steps` One object of the present inventionis to develop improved method and means for separating iinely dividedand slow-separating suspended foreign material from liquid containing`the same, particularly such method and means for separating digest mudfrom mixtures with aluminum sulfate liquors obtained in the sulfuricacid-clay digestion method for manufacturing alum.

The invention and the manner in which the objects stated above areaccomplished may be understood by considering the drawings in which likereference numbers designate equivalent iparts on the various figures.

Figure l represents an elevation View of one type of machine of thepresent invention with part of the machine broken away and shown insection. Figures 2 and 3 are vertical and horifzontal sections,respectively, of the central element ofthe rotor of the Figure lmachine, illustrating certain variations of the invention. Figluref4is'an elevation viewof another'type of machine built according to thepresent invention with certain portions thereof broken-away and shown insection. Figure 5 is a vertical section taken at plane 5-5 of Figure 4.

The invention will first be described in connection with Figure 1, whichrepresents one embodiment. The stationary housing of the machineisindicated generally at IEB .and is securely mounted on supportingbrackets not shown. Spider Il supports bearing i2, within which turnsshaft l5 driven by belt and pulley lli. Shaft i5 extends throughstationary collar Il and is attached at the bottom end to head piece2li. Head piece 20 has Aa radially disposed apron or skirt 2l havingribs 22 which interlock with ribs 25 on basket or bowl 26, therebytransmitting motion from shaft l5 to basket 2E. Lock ring 2l is providedto permit-dismantling of the centrifugeibasket 26 when desired. Sleeve3l which surrounds shaft I5 and the upper part of head 2E is supportedonskirt 2i and spaced therefrom byknobs 40. Sleeve 3l supports, in turn,conical .discs 46 which are spaced from each other by knobs or detentsi8. The weight of basket 26 and its contents arecarried by skirt 2l andshaft l5. The outermost periphery of basket 25 is provided with multiplespaced nozzles 42, communicating with discharge manifold 5i, leading inturn to recirculating line i2-t via ports 53 in the manifold. The rotor,or rotating portion of the centrifuge machine Comprises shaft'l, head2B, basket or bowl 2t, sleeve 3l and discs 46.

According to the present invention, feed material containing liquid andsolid material to be separated, preferably after preliminary settling orclassification to remove the largest of the insoluble particles(primarily to reduce attrition on metallic parts) and toprevent pluggingnozales ft2, is introduced through pipe 35i and enters the annular space3l between stationary collars l1 and 32. It will be understood that upuntil the time the feed material reaches approximately the point 35 atthe outlet of annular passage 3l, lthe liquid is still flowing in aksaid zone having .an Aappreciable radial comp'oneht of-directio'n andin A`which the liquid is nrst subjected to'rapid'rotation and resultantshearing. The liquid feed passes underneath the bottom edge of sleeve 3l(supported on head 2li by multiple knobs lill) and enters separatingzone ci of enlarged radial dimension. The present invention provides forsupplying ilocculating agent to the feed slurry at such a point in thesystemL that the material within separating zone ii is subjected tofiocculation and the effect of enhanced separation of solid particlesfrom liquid produced by reason of the presence of said agents. Highcentrifugal force in separating zone el produced by the high rotationalspeed of basket 2GB, coupled with the enhanced ooculating effect of theagent produce the advantageous separation of lines from liquid according to the present invention whereby solid material is induced to passthrough multiple nozzles d2 while substantially clear solution or liquidpasses through passageways 155 between inclined discs 5. Discs i6 assistclarification of the liquor by providing surface on which the solidparticles can settle and inducing by friction outward movement ofparticles of insolubles that come into contact with the discs. heliquid, under the hydrostatic head of the feed introduced at 3E, passesupwardly through the annular discharge passage between sleeve 3i andbasket 2E and over discharge lip il at the top of the basket and intodischarge conduit 5cl Part of the underflow discharged through nozzlesi2 and entering manifold 5| and recirculating pipe 52 is normallydischarged through valve and pipe 55 and part is normally recirculatedvia pipe 5S and port 5l in the bottom of basket 2@ as indicated by theflow arrows. The recirculated liquid passes through apertures betweenskirt 2| and bowl 26 into separating zone 4| as shown. Wash liquid maybe introduced through valve and piping et if needed.

A particular feature of the discovery of the present invention is thatby introducing ilocculat ing agent into the feed stream in such a mannerand at such a point in the stream as to effect dispersion of theiiocculating agent through the liquid downstream from the point at whichsaid feed is first subjected to shear, remarkably iniproved separationof solid from liquid is realized. Pursuant to this feature of thediscovery inlet pipe ci, communicating with the annular' passage betweenrotating shaft i5 and stationary collar Il, is provided. Through thispipe the flow of fiocculating agent, supplied from vessel 62 controlledby valve 65 and metered at S5, is supplied. This stream of flocculatingagent is added to the main flow of feed material from pipe 3D at thepoint at which said feed flow is first subjected to the shearing actionaforesaid. Since an appreciable interval of time is required to effectdissemination of the occulating agent through the feed material, it isapparent that dispersion of the flocculating agent through the liquid iseffected downstream from the point at which the feed is rst subjected toshear. The stream of liquid, now comprising feed plus ilocculatingagent, passes downwardly through inlet zone 35, under the bottom ofsleeve 3l and into separating zone 4| where enhanced eifect of theocoulating agent in separating solid from liquid is utilized asdescribed above. Broadly considered, the invention comprises addingflocculating agent at any point between 35 (where the feed is firstsubjected to shear) and the discharge of separating zone 4|, preferablysuihciently adjacent to the point of rst shear to permit adequatecentrifuging of the feed to effect dispersion of the flocculating agentin zone 36 and separation of solid in zone 4| before discharge of liquidand solid from separating zone 4|. A particular embodiment of theinvention comprises adding fiocoulating agent prior to the point atwhich the stream enters separating zone fil, i. e. be tween points 35and de which dene the radially directed inlet zone.

Modifications of the invention are illustrated in Figures 2 and 3 whichprovide for introduction of iiocculating agent through axially disposedpassageway El in shaft I5 and subsequent flow of the agent throughmultiple radial passages lil in head 25. The feed material is firstsubiected to shear above the outlet of passage lil and hence thefiocculating agent and feed are mixed in inlet zone SiS after the pointat which the feed is first subjected to shear.

A further embodiment of the invention provides for removing threadedplugs 12, inserting similar plugs in passageway l and provide for iiowof occulating agent only through radial passageways '12. The latterarrangement also contemplates introducing the flocculating agent withininlet zone 35 after the feed is first subjected to shear and before thefeed enters separating zone l.

Figure 4 represents a different, i. e. horizontal type centrifugalmachine constructed according to the present invention. Pulley 85,driven by belts and motor not shown, is connected via flange BS tocylindrical sleeve 8'.' rotating on bearing 9B within pillow block Si.Sleeve 8'! is connected to centrifugal basket indicated generally at 92,housed in stationary casing 93, said basket come prising cylindricalsection 95 and end wall sections 96 and 91, all of which are adapted torotate at high speed about their horizontal axes. Vtfall section @l isconnected to sleeve Hit which engages a gear unit not shown on thedrawing. The motion of pulley S5 and bowl or basket $52 is transmittedthrough said gear unit to internal shaft lGi (separated from shaft I bypacking |82), trunnion |135 and conveyor hub it. At its opposite end,hub Hifi is connected to internal sleeve lill', which rides on bearings|I|- and is separated from shaft 8'1' by packing Hi. Hub |68 is providedwith helical conveyor blades H2 which, by reason of the slight relativerotation between bowl 32 and hub it, adapted to move material within thebowl to the end of the machine represented by the left end of the Figurefr drawing.

Feed slurry (preferably after preliminary settling or classification toremove the largest particles of solid) enters the machine through pipe ii5 and passes through the annular space between inner wash pipe |16 andpipe il?. The feed emerges from said annular space and en ters inletzone H8 formed between the outlet of pipe il and separating zone l2?.The feed first falls into pool i2@ on the inside of hub |86 and betweenpartitions |2| and |22, said pool being in the form of a cylinder byreason of centrifugal force. Feed liquid overflows from pool 52D intomultiple overflow pipes |25 and enters separating zone |27 internally ofbowl 92. Pipes 52d, which facilitate rotational flow of liquid therebyminimizing disturbance of the liquid as it enters pool E32 in separatingzone |21 may be short as shown in Figure 4, or may extend into pool |32.Due to high centrifugal force, the denser solid particles of the mudtend to concentrate on the inner surface of cylinder 95 and are pushedto the left forming bed |28 which is discharged over a Weir 30 into theunderflow connecting manifold 3| in stationary casing 93. Underiow isforced from manifold |3| by means of plow |33 attached to end Wall 91and discharged from manifold I3! through a port not shown, near thebottom of the casing.

'Ihe overnovv from bowl S2 builds up in pool |32 in separating zone l2?and the clear liquid near the axis of bowl 92 overflows throughdischarge ports |35 into overflow collecting manifold |31 in casing S3.rThe overiiow is likewise withdrawn from the casing through a port nearthe bottom of the casing which is not shown in the drawing.

In the manner indicated above, the present invention provides forsupplying an agent having iiocculating properties in separating zone l2?land subjecting the feed while in said zone to the combined action ofsaid agent and centrifugal force thereby markedly to increase theeffectiveness of the centrifugal force in separating the materials ofdifferent densities, i. e. the less dense liquid and the relatively moredense dispersed solid. The liquid flowing through the Vannular spacebetween pipes I8 and Ill is non- -rotating as distinguished fromrotational iovv,

i. e. the flow of a body of rapidly rotating liquid in a centrifugemachine. The stream is'rst subjected to the shearing action as it enterspool 42d, Accordingly, the invention broadly comprises addingiiocculating agent in the region from pool |29, to discharge ports |36preferably in inlet zone H8.

A particular embodiment of the invention com.- prises supplying anadditional partition |38 to the right of partition i212 forming a zoneM0. containing flocculating agent in pool Idl which overiiows throughmultiple radially disposed distributing pipes m2 into separating zonel2?. Pipes m2 which may be short as shown or may extend into pool |32facilitate rotational flow of flocculating agent entering pool i3d,thereby minimizing disturbance of the liquid. Flocculating agent issupplied to Zone i2? through feed pipe lil@ which communicates withannular passage |41 between external pipe its and pipe l l1, said.annular passage discharging into pool fil. A flow of flocculating agentfrom pipe ifii is established from storage vessel E50 Via flow controlvalve |5| and meter |52. According to the latter embodiment of theinvention, fiocculating agent and feed are first mixed substantially atthe end of inlet Zone lid, i. e. after the feed is first subjected toshear so as to permit dispersion of agent through the feed after iirstshearing the feed liquid.

A further embodiment comprises omitting partition so that riocculatingagent from annular space ifi'i enters pool '12B directly, therebyeffecting dispersion of occulating agent through the feed liquid afterthe point at which the feed is rst subjected to shear, i. e. pool |20.The mixture thereafter fl ws through pipes |25 (preferably elongated toreach pool |32) into the pool. If desired, pool ld and distributionpipes i2 also may be dispensed with and feed and flocculating agentpermitted to fall directly into pool |32 in separating zone i2?. It willfurther be noted that, in accordance with the principles stated above,introducing iiocculating agent into pool i2@ or directly into pool E32provides for addition of agent in the region from the point at Which thefeed is first subjected'to shear (pool or pool |32, as the case maybe)to overow pipe |35 at the discharge end ofseparating zone 'Asexemplifying the size of machinesuitable for the purpose of the presentinvention, in the Figure 1 apparatus, the inside diameter of the .basket26 may be 9 inches. The distance from port 51 to discharge lip el' maybe 9% inches. The outside diameter of apron 2| may be 6% inches. Theapproximate length of inlet Zone 3E, i. e. between points 5 and i0 maybe 5 inches. Separating zone d! may have capacity of 2 gallons. Discs 46may be 28 in number, disposed at 45 from the horizontal and l-Z- incheslong in section. With respect to the Figure 4 apparatus, cylinder 95 may18 inches in diameter and the distance between end walls iii and Si' maybe 28 inches. Separating .Gone i2? ymay have capacity of 5 gallons. TheFigure l apparatus may suitably operate at about ddd@ to 9000 r. p. m.,thereby producing centrifugal force of 5460 to 19,003 times gravity; andthe ie e apparatus operated at 2000 to 2500 r. p. m. thereby producing aforce equal to 1000 to i500 times gravity. The principle of thisinvention applies when operating u ithany elevated degree of centrifugalforce, but lower forces generally require longer retention time in theseparating zone, as described below. Hence it is preferred to operatewith centrifugal force not less than about 100) times gravity. The use0f this invention is not limited to machines of the above dimensionssince such dimensions vary in accordance with type and size ofequipment.

The foregoing method and apparatus have general application where it isdesired to separate nnely divided insoluble material from liquidcontaining the Specific instances for using the present inventioninclude recovery of sulfuric acid from sludge obtained via scrubbingimpure sulfuric acid synthesis gases; removal of gypsum from phosphoricacid in the manufacture thereof by treatment of phosphate rock withsulfuric acid; removal of solids from mixtures resulting from thetreatment of aluminous materials with acids and allralis; and recoveryof oxide of titanium from ilmenite ore.

The flocculating agent employed in each instance may depend largely onthe particular foreign materiai to be removed and the particularsolution to be clarified. Suitable flocculating agents which bementioned include prosein (a protein material derived from soya bean)gluesuliide (equal parts of animal glue and sodium sulfide) and animalglue alone. In each case the flocculating agent is first dispersed in asuitable solvent such as water to facilitate distribution thereofthrough the material to be treated.

It has been found that the method and apparatus outlined above may beadvantageously applied to separation of aqueous aluninum sulfatesolutions from insolubles in the manufacture of aluminum sulfate by thesulfuric acid-clay digestion process. In the commercial process formaxing aluminum sulfate from clay or other aluminous material, thestarting material, either in the raw state or after calcination toremove water and render the clay more susceptible to subsequent attackby sulfuric acid, is digested with strong sulfuric acid to convert thecombined aluminous materials in the clay to aluminum sulfate. rTheproduct of digestion is diluted with water or Weak aluminum sulfatesoiution to dissolve out sought-for aluminum sulfate. The slurry soformed is introduced into large settling tanks to permit undissolved andinsoluble portions of the clay (referred to as digest mud) tosettleuntil'theheight of the-mud level drops to about or less of the totalcolumn of diluted reaction mixture. Clear supernatent liquor isWithdrawn through stand pipes and concentrated in steamheatedevaporators to alum, cake strength. The mud may be reslurried in Waterand subjected to resettling to recover' aluminum sulfate present in mudliquor. The solid particles of the digest mud are generally in such afine state of subdivision that use of prolonged periods of settlingprior to decantation, e. g. up to 24 hours or more in some cases andconsequent large volumes of settling-decantation vessels arenecessitated. .ficcording to the present invention, more eifectivc andefficient recovery of clear aluminum sulfate solution from aluminumsulfate slurries may be realized Without incurring the disadvantages ofincreased steam costs for evaporation or excessive investment in undulylarge settling tanks which were inherent in previously proposed methodand means (i. e. dilution of slurry to increase density differences andthereby speed settling) for improving recovery of aluminum sulfate.

It has been found that in the case of aluminum sulfate recovery, animalglue is a particularly eiiective locculating agent, said glue being usedaccording to the method and means described generally and in detailabove. Hence, one specific embodiment comprises supplying means for andutilizing glue as iiocculating agent in recovery of aluminum sulfatefrom slurries according to the invention described above. For example arapidly rotating body of liquid is maintained in a centrifuge machineand a non-rotating stream of slurry7 to be centrifuged is added to therotating body thereby to create a zone of shear between the feed ofnon-rotating slurry and the rotating liquid. Centrifuged clear liquid iswithdrawn from the rotating body. An aqueous glue solution is introducedto the rotating body of liquid substantially in the region but after thepoint at which the slurry feed stream is first subjected to shear uponintroduction into the rotating body of liquid undergoing centrifuging.

The ilocculating agent, e. g. glue used in amount sufdcient to effectthe degree of removal of insolubles desired. Excessive amounts of gluedo not appreciably increase the emciency of clariiication. A suitableconcentration range of glue in the aluminum sulfate solution affordingusual enicient operation without undue Waste of glue is 0.50 to 1.12grams of dry glue per gallon of solution to be clarified.

A further signiiicant variable is the concentration of glue in the gluesolution to be added to the slurry. In concentrations below about 0.1lb. of dry glue per gallon of Water appreciable decrease ineffectiveness of the fioccuiating agent may be noted and henceconcentration is preierably maintained not less than about 0.1 lb. ofdry glue per gallon of water. To facilitate dispersicn oi thelocculating agent into and through the process material and efficientutilization of glue, concentration of glue in the solution is preferablymaintained not greater than about 0.2 lb. per gallon of Water althoughhigher concentration may be used ii desired. By maintaining gluesolution concentration in the range approximately 0.1 to 0.2 lb. pergallon of water, adding such solution at the rate of about 30 cc. ormore per gallon of aluminum sulfate slurry to be clarified, according tothe technique outlined above, effective clarification of the aluminumsulfate digest mud may be obtained.

The slurry being treated is retained in the centrifuge machine under theinfluence of flocculating agent and centrifugal force for time sumcientto effect the degree oi clariiication desired. As previously indicated,the effect of centrifugal force producing separation of insolubles isaided by the presence of discs in the separating zone, and hence theretention time required for eective clarification Will be determined bythe presence of the discs as Well as the centrifugal force. lTheretention time, of course, Will be controlled by the rate of flow offeed material and influenced by the volume of the centrifuge bowl or .itwill be understood that generally, large volume machines willaccommodate larger ilow rates While still affording the requiredretention time and, conversely, small volume machines will normallyaccommodate only smaller oW rates. Using a machine of the type describedin Figure l, having dimensions and operating according to the proceduredescribed above, retention time of the order of 0.56 to 0.25 minute(corresponding with rates of now of feed of 3 to 8 G. P. M.,respectively) may be found to produce suitable olariiication. Operatingwith the type of machine described in Figure i. having dimensionsindicated above and operating according to previously describedprocedure, retention times in the range approximately 5 to i minutes(corresponding with feed rates ci 1 to 5 G. P. M., respectively) niay besuitable. For any given installation and set of conditions, retentiontime and rate of flow of feed may best be determined by making test runsand noting results.

Requirements oi product quality may vary, but in manufacture of highgrade alum, it is preferred to reduce content of insoluble in theclaried solution to below about 0.1% (corresponding with about .25%based on the nal 17.2% 1.12633 solid product). Eiilciency ofclarification may be measured by the volume ratio of overflow havingacceptable clarity to underflow (containing the majority of theinsolubles). In the interest of high capacity and eificient operation,and to reaiize advantages of the invention, conditions are preferablymaintained so as to produce volume ratio of overiiow (having not morethan about 0.1% insolubles) to underflow not less than about 3.

rShe apparatus and procedure of this invention were found to beeifective in clarifying aluminum sulfate solutions of substantially anyAMSOQS strength, e. g. in the range 1 B. to 40 B. Within the limits oioperativeness of the iiocculating agent, the procedure may be carriedout at any temperature, i. e. temperatures as lov.l as '70 F. and ashigh as 200 F. have been found to be suitable in clarifying aluminumsulfate digest muds with glue as flocculating agent.

The clarification procedure of the invention has been described chieflyas being carried out continuously, but batchwise operation is notthereby excluded. For example, a batch of feed material may beintroduced to the centrifuge basket, a proportionate amount ofilocculating agent added thereto, the mixture centrifuged, sedimentremoved from the basket and the clariiied solution subsequentlyrecovered.

Although this invention is not limited to any speciiic theory, I believethat the occulating agent in some fashion probably causes agglomeraticnor flocculation of the finely divided and slow settling particles intorelatively larger, more rapidly settling agglomeraties or ilocls,thereby facilitating separation of insolubles from the body of thesolution. When the feed stream passes t rough the zone of shear uponentering the rotating'basket oi the centrifuge, any such flocks oragglomerates previously formed are somewhat disintegrated, therebydiminishing the previous beneiicial result of flock formation. Hence,according to a particular embodiment of the invention, by addingrlocculating agent in the region from the point where the feed stream isfirst subjected to shear to the separating zone, the docks oragglomerates after once being formed are not subjected to furthershearing or other violent agitation which might result in breaking up ofthe agglomerates. Hence, the effect of flock formation .in improvingsettling characteristics is preserved until the suspension reaches theseparating zone wherein insolubles and solution are separated from eachother.

The following example illustrates practice of the present inventioncarried out with apparatus described in Figure l., the parts andpercentages being weight.

Erw/cple The sulfate. slurry chosen for test was produced by .l lurcacidtreatment of calcined clay. Frio-r to centriuging, the slurry waspermitted to settle for a shorJ time to remove the largest particiesvofinsolubles. This slurry, hav' 3.8% solids, aluminum sulfate content eq.aient to 8.48% AlzOe. and speciic gravity of 37.10 at 60 F., wasintroduced at the rate of 5.1i G. P. M. through feed pipe 3e of theFigure 1 apparatus. rihe feed temperature was 190 F. (34.6 B). rThemachine speed (no load) was 6,5m R. P. lvl. Nogales i2 were .052 inch indiameter. in aqueous glue solution containing 1.5 at glue on a dry basiswas introduced through pipe Si at the rate of 30 cc. per minute pergallon aluminum sulfate slurry (corresponding with 0.001 lb. per minuteof dry glue per gallon aluminum sulfate slurry). No wash Water wasintroduced through pipe and valve Underow was withdrawn from pipe andvalve at the rate oi 1.3 G. P. M. and overiiow through pipe t at therate of 4.1 G. P. M. With these conditions the overflow contained 0.06%solids (which corresponded with 0.3% solids based on the 17.2% A1203aluminum sulfate produced after evaporation of the solution) and was35.5 B. at 60 F. The underiiow contained 17.3% solids and was 37.8 Be.at 60 F. The percentage of feed solution recovered in the overflow was80% and the recovery oi solids in the underflow was 99%.

The foregoing example illustrates single pass operation. If desired, theunderiiow, containing substantially all of the solids and a certainamount of the aluminum sulfate present in the orieinal feed, may bereslurried with additional water, then treated again in a separatecentrifuge machine with additional occulating agent to eiect recovery ofresidual amounts of aluminum sulfate. By such treatment of digest mudsin a series of centrifuging operations, any desired proportion, e. g.preferably $38 to 99%, of the original aluminum sulfate may be recoveredas clear aluminum sulfate solution.

I claim:

l. A two zone continuous method for separating iinely divided suspendedsolid material from liquid containing the same which comprises in afirst dispersing zone rotating a body of said liquid containing finelydivided suspended solid material without substantial turbulence about anaxis in a dispersing zone disposed near said axis at a linear velocitysuiicient to eect dispersion of addediiocculating agent to the rotatingbody` of liquid in thedispersing Zone without effectingl substantialseparation of suspended material from the liquid in said dispersingzone, continuously introducing a non-rotating stream of. liquidcontaining finely divided suspended material to the dispersing Zonethrough conduit means located near said axis thereby to create a Zone ofshear between said feed of non-rotating liquid and said rotating liquidin said dispersing Zone, continuously introducing through axiallydisposed conduit means a flocculating agent to said rotating body ofliquid in the dispersing zone after the point atA which said feed liquidis first subjected to shear, continuously flowing the liquid containingiinely divided suspended solid material and dispersed occulating agentfrom the rst rotating body of liquid in the dispersing zone Withoutsubjecting said liquid to shearing and violent agitation which wouldresult in breaking up of iocs to a second separating zone containing abody of liquid rotating about the axis at a higher linear velocity thanthe rotating body of liquid in the rst dispersing zone and withsuiiicient velocity to eiiect separation or" neiy divided suspendedsolid material from the liquid by centrifugal iorce, continuouslyremoving said seprated solid materialirom the secondzone, andcontinuously discharging clarified liquid from the second zone.

2. A two zone co tinuous method for recovery of aluminum sulfatesolution from liquid containing the same and insoluble mate 1iaiproduced in the suliuric acid-clay digestion process for manufacture ofaluminum sulfate, which comprises in a rst dispel-sing zone rotating abody of aluminum sulfate solution containing insoluble material withoutsubstantial turbulence about an axis in a disp-ersing zone disposed nearsaid axis at a linear velocity sucient to eiect dispersion of addedflocculating agent to the roeating body of liquid in the dispersing zonewithout effecting substantial separation or" suspended material from theliquid in said dispersing zone, continuously introducing a non-rotatingstream oi' aluminum sulfate liquid containing insoluble material to thedispersing zone through conduit means located near said axis thereby tocreate a zone oi` shear between said feed or" non-rotating liquid andsaid rotating liquid in said dispensing zone, continuously introducingthrough axially disposed conduit means a occulating agent to saidrotating body of liquid in the dispensing zone after the point at whichsaid feed liquid is nrst subjected to shear, continuously iiowing thealuminum sulfate liquid containing insoluble material and dispersediiocoulating agent from the rotating body of liquid in the rstdispersing zone without subjecting said liquid to shearing and violentagitation which would resuit in breaking up of ocs to a secondseparating zone containing a body of aluminum sulfate liquid rotatingabout the axis at a higher linear velocity than the rotating body ofliquid in the first dispersing zone and with sufficient velocity toeiiect separation of suspended material from the liquid by centrifugalforce, continuously removing said separated solid material from thesecond zone, and continuously discharging clarified aluminum sulfateliquid from said secondzone.

3. A two Zone continuous method for recovery oi aluminum sulfatesolution from liquid containing the same and insoluble material producedin the sulfuric acid-clay digestion process 11 for manufacture ofaluminum sulfate, which comprises in a rst dispersing zone rotating abody of aluminum sulfate solution containing insoluble material withoutsubstantial turbulence about an axis in a dispersing zone disposed nearsaid axis at a linear velocity sufiicient to eiect dispersion of addedflocculating agent to the rotating body of liquid in the dispersing zonewithout eiecting substantial separation of suspended material from theliquid in said dispersing zone,

continuously introducing a non-rotating stream of aluminum sulfateliquid containing insoluble material to the dispersing zone throughconduit means located near said axis thereby to create a zone of shearbetween said feed of non-rotating liquid and said rotating liquid in`said dispersing zone, continuously introducing through axially disposedconduit means a flocculating agent comprising an aqueous glue solutionof concentration in the range of 0.1 to 0.2 lb. dry glue per gallon ofwater and in amount corresponding with 0.50 to 1.12 grams of dry glueper gallon of aluminum sulfate liquid feed to said rotating body ofliquid in the dispersing zone after the point at which said feed liquidis rst subjected to shear, continuously flowing the aluminum sulfateliquid containing insoluble material and dispersed iiocoulating agentfrom the rotating body of liq- References Cited in the le of this patentUNITED STATES PATENTS Number Name Date 1,356,665 Sturgeon Oct. 26, 19201,525,016 Weir Feb. 2, 1925 1,546,871 Thompson July 21, 1925 1,604,427Spicer Oct. 26, 1926 2,111,788 Klchma Mar. 22, 1938 2,128,393 Allen Aug.30, 1938 2,138,463 Ayres Nov. 29, 1938 2,190,596 Dorr Feb. 13, 19402,245,587 Hughes July 17, 1941 2,312,545 Haug Mar. 2, 1943 2,553,936Patrick May 22, 1951

